Detailed descriptions of many of the study populations are in Chapter 2 of Veterans and Agent Orange (hereafter referred to as VAO) (IOM, 1994), and the criteria for inclusion in the review are discussed in Appendix A of that report. The studies reviewed addressed exposures to 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and its contaminant TCDD, cacodylic acid, and picloram. The committee also examined some studies that addressed compounds chemically related to the herbicides used in Vietnam, such as 2-methyl-4-chlorophenoxyacetic acid (MCPA), hexachlorophene, and chlorophenols, including trichlorophenol. In other instances, investigators did not indicate the specific herbicides to which study participants were exposed or the magnitude of exposure; these complicating factors were considered when the committee weighed the relevance of a study to its findings. If they were available, details of exposure assessment and use of exposure in the analysis are discussed in Chapter 5.

The occupational section covers studies of production workers, agricultural and forestry workers (including herbicide and pesticide appliers), and paper and pulp workers. The environmental section covers studies of populations accidentally exposed to unusual concentrations of herbicides or dioxins as a result of where they live, such as Seveso, Italy; Times Beach, Missouri; and the southern portion of Vietnam. The section on Vietnam veterans covers studies conducted in the United States by the Air Force, the Centers for Disease Control and Prevention (CDC), the Department of Veterans Affairs (VA), the American Legion, and the state of Michigan; it also notes studies of Australian Vietnam veterans.

Many cohorts potentially exposed to dioxins and the herbicides used in Vietnam are monitored periodically, typically every 3–5 years (such as the cohorts of the National Institute for Occupational Safety and Health (NIOSH), the International Agency for Research on Cancer (IARC), the National Cancer Institute (NCI), Seveso, and Ranch Hand). For the sake of thoroughness, the discussions of specific health outcomes in Chapters 6–9 include references to studies discussed in previous Agent Orange reports and new studies, but in making its conclusions, the committee focuses on the most recent update when multiple reports on the same cohorts and end points are available.

Individual researchers who are a part of research consortia evaluating cohorts in large multicenter studies (such as the IARC and NCI cohort studies) sometimes publish reports based solely on the subset of subjects they themselves are monitoring. All the studies are discussed in this report, but when making its conclusions, the committee focuses on the studies of the larger, multicenter cohorts.

OCCUPATIONAL STUDIES

Several occupational groups in the United States and elsewhere have been exposed to the types of herbicides used in Vietnam and to TCDD. Occupational

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